The present invention relates to release liners comprising a thermoplastic film having a cured silicone coating which provides a liner release surface, moldable pressure-sensitive adhesive fastening tapes including such release liners and to the use of the release liners and tapes in laminates including a moldable or formable layer which may be molded by application of heat and pressure.
The release liner may be used to protect or cover a surface of the laminate to be molded. The release liner is particularly useful in the molding of laminates including a formable layer comprising a flat workpiece or sheet material blank and a pressure-sensitive adhesive layer having an outer surface covered by the release liner. Of course, the laminate may be provided by the combination of a formable layer and a fastening tape comprising the pressure-sensitive adhesive layer and release liner. The desired degree of adhesion or releasability of the liner is provided by the silicone coating on the release surface of the liner. In such molding applications, it is necessary to achieve both good mold conformability and retention of uniform releasability.
In present practice, the release liner does not itself consist of a moldable material and the liner may tend to assume a non-conforming shape which includes wrinkles or folds. Poor mold conformability is encountered in the molding of complex shapes as well as even relatively simple shapes involving non-uniform extension of portions of the laminate. Typically, release liners including a paper layer are unsatisfactory since they do not provide sufficient elongation to accommodate complex mold shapes which may include surfaces defined by compound curves and/or require extension of laminate portions in angularly intersecting directions.
The molding process tends to increase the adhesion or release force between the release liner and the surface to which it is secured. The exact phenomenon of the undesirable increase in release force is not known, but it is deemed to be a change in the release surface and/or silicone coating due to migration of silicone away from the release surface of the liner and/or penetration of the release surface by the pressure-sensitive adhesive.
The present invention has been found especially advantageous in the thermoforming of carpet materials including a pressure-sensitive adhesive layer for installation of the molded carpet. Various thermoforming techniques are discussed in Irwin, Dave, Introduction to Thermoforming, Modern Plastics Encyclopedia, pp. 286-292, 1988. In the thermoforming of carpet materials, a matched mold forming technique is used with the carpet material being shaped in a clearance between the closed mold halves. The carpet is heated to a temperature in the range of 200.degree. F. to 450.degree. F. and then molded at a pressure of several thousand psi. Applicants are not aware of any successful prior release liners or techniques for thermoforming a carpet, pressure-sensitive adhesive and release liner laminate.
U.S. Pat. No. 4,405,668 discloses the use of pressure-sensitive adhesive coated fiber strands embedded in the backing of carpet materials for installation thereof after removal of a polyethylene sheet release layer. This patent also proposes automotive interior applications wherein the carpet materials are molded following the removal of the polyethylene sheet release layer in order to simultaneously effect the molding and adhering of the carpet material.
U.S. Pat. No. 2,986,777 discloses a carpet molding technique for automotive interior floor carpets. The carpet is molded or shaped between mating dies to set the back of the carpet. This patent does not disclose the use of an installation adhesive for the carpet.
The use of a plastic film such as polyethylene film at a mold surface to improve the surface of a poured concrete part and better conform the part surface with the mold is disclosed in U.S. Pat. No. 4,331,628. The plastic film is heat-softened and a vacuum is applied to make the film better conform to the mold surface.
U.S. Pat. No. 2,343,930 discloses a creped web coated with plastic which is melted during molding to carry the web to a more exact mold shape. U.S. Pat. Nos. 4,350,551 and 4,443,507 disclose molding processes wherein an intermediate layer of a thermoplastic or thermosetting film is melted during the molding process to accommodate relative movement between adjacent layers.